This requires 2 parts. The actual library file that's very simple put this in your CR2, Pose or what ever:

---

{
        version
    {
        number 12
    }
    runPythonScript "WhateverYouCalledTheReadme.py"
}

---

The second part can be as fancy or simple as you like. The easiest is to just use Poser's "Simple dialog" for the text thus:

---

import poser

poser.DialogSimple.MessageBox("This is my super interesting description")

---

Put the python that contains your text in the came library folder as the actual library file. Like this ...

Now if that's not fancy enough for you can open a web browser the same way ...

---

import poser

try:
    import webbrowser
    webbrowser.open_new("http://www.mycoolwebsite.com/MyAwesomeReadme.html")
except:
    MessageBox("There's a problem, please visit http://www.mycoolwebsite.com/MyAwesomeReadme.html")

---

The web page can be anything the browser can display.

P.S. This is how the vendor links that are in some products work. They just link to the vendors store page instead of a readme.